PURPOSE: To prevent a gear teeth surface from being worn by feeding oil to the teeth surface of a sun gear even when the rotational speed of a planetary gear becomes high.

CONSTITUTION: A ring groove 5 is drilled around a shaft at the side surface of a pinion gear 10, and a communicating hole 55 which can communicate the outer periphery side of the groove 5 with the tooth surface of the pinion gear 10 is formed. There is also provided, in the groove 5, a shielding ring 3 which can slide to shield the communicating hole 55, and a weight 1 is installed on a part of the shielding ring 3 to form a cut part 7 on the opposite side of the weight. While the pinion gear 10 and a pinion carrier 12 are rotating, the weight 1 is positioned on the outer periphery side by the centrifugal force which is generated by the rotation of the pinion carrier 12. The cut part 7 always faces the sun gear 6 side, so oil which stays in the groove 5 by the centrifugal force which is generated by the rotation of the pinion gear 10 is fed to the sun gear from the communicating hole 55 on the sun gear side.